1. Field of the Invention
The present invention relates to an inkjet printhead and a manufacturing method thereof, and more particularly, to a bubble-jet type inkjet printhead having improved structures of an ink chamber and ink channels, and a manufacturing method thereof.
2. Description of the Related Art
Ink ejection mechanisms of an inkjet printer are largely categorized into two types: an electro-thermal transducer type (bubble-jet type) in which a heat source is employed to form bubbles in ink to eject the ink, and an electro-mechanical transducer type in which ink is ejected by a change in ink volume due to deformation of a piezoelectric element.
According to a bubble growing direction and a droplet ejecting direction, electro-mechanical transducer types are classified into top-shooting, side-shooting, and back-shooting types. In a top-shooting type printhead, bubbles grow in the same direction that ink droplets are ejected. In a side-shooting type printhead, bubbles grow in a direction perpendicular to the direction that ink droplets are ejected. In a back-shooting type printhead, bubbles grow in a direction opposite to a direction in which ink droplets are ejected.
A bubble-jet type inkjet printhead needs to meet the following conditions. First, a simplified manufacturing process, a low manufacturing cost, and mass production must be allowed. Second, in order to produce high quality color images, creation of minute satellite droplets that trail ejected main droplets must be prevented. Third, when ink is ejected from one nozzle or an ink chamber is refilled with ink after the ink ejection, a cross-talk between the nozzle and its adjacent nozzle through ink which is not ejected, must be prevented. To this end, a back flow of ink, that is, a phenomenon that ink flows in an opposite direction to a normal ejection direction, must be avoided during the ink ejection. Fourth, for a high speed printing, a refill cycle after the ink ejection must be as short as possible. That is, an operating frequency must be high.
Considering the above conditions, the performance of an inkjet printhead is closely associated with structures of the ink chamber, ink channels, and a heater, the type of formation and expansion of bubbles, and the relative size of each component.
FIG. 1 is a schematic cross-sectional view of a conventional inkjet printhead disclosed in a U.S. Pat. No. 6,019,457.
Referring to FIG. 1, an ink chamber 15 having a hemispherical shape is formed in an upper portion of a substrate 10 made of silicon, etc., and an ink supply manifold 16 supplying the ink chamber 15 with ink is formed in a lower portion of the substrate 10. An ink channel 13 communicating with the ink chamber 15 and the ink supply manifold 16 is formed between the ink chamber 15 and the ink supply manifold 16.
A nozzle plate 20 having a nozzle 11 through which an ink droplet 16 is ejected, is disposed on a surface of the substrate 10 to form an upper wall of the ink chamber 15. The nozzle plate 20 includes a thermal insulation layer 20a and a chemical vapor deposition (CVD) overcoat layer 20b. 
In the nozzle plate 20, an annular heater 12 surrounding the nozzle 11 is formed in the vicinity of the nozzle 11. The annular heater 12 is located at an interface between the thermal insulation layer 20a and the CVD overcoat layer 20b. Meanwhile, the heater 12 is connected to an electric line (now shown) through which a current pulse is supplied to the annular heater 12.
In the above-described configuration, in a state that the ink chamber 15 is filled with ink supplied through the manifold 16 and the ink channel 13, if the current pulse is supplied to the annular heater 12, heat generated by the annular heater 12 is transmitted through the underlying thermal insulation layer 20a, and the ink under the heater 12 is boiled to form a bubble B. Thereafter, as the heat is continuously generated from the annular heater 12 so that the bubble B expands, a pressure is applied to the ink contained in the ink chamber 15, and the ink around the nozzle 11 is ejected in a form of an ink droplet 18 through the nozzle 11. Then, new ink is introduced through the ink channel 13 to refill the ink chamber 15.
In the conventional inkjet printhead, since the ink chamber 15 has the hemispherical shape and is formed on the substrate 10 by isotropically etching, the degree of accuracy and reproducibility of the inkjet printhead deteriorates when the ink chamber 15 is manufactured. Also, the amount of ink contained in the ink chamber 15 is relatively small in view of a volume of the ink chamber 15. Also, the hemispherical ink chamber 15 is configured such that the ink may be easily ejected to the ink channel 13 in a case where the ink around the annular heater 12 is pushed away by a bubble pressure caused when the bubble B is formed. When the ink is ejected, and when the bubble B is contracted, it is difficult to smoothly refill the ink chamber 15 with the new ink.
Although the ink channel and the nozzle are aligned to make an ink flowing direction substantially linear, a problem occurring in the aforementioned conventional inkjet printhead is that the ink flow is not smooth during the ink ejection. This results in undesirable frequency characteristics of the inkjet printhead.
Since only a single ink channel is formed for each ink chamber, it is difficult to adjust a transferring amount of ink passing through the ink channel. A manufacturing process of such an ink channel is also complicated.